The warden in my group logically argues, that he should be able to designate the group's infernal warlock, who is an extremely capable guy and has beaten the other in more than one 1vs1, as his bonded charge.
However, the rest of the sentence reads

3 Answers
3

First, consider that from an optimization standpoint Guardian is considered a very strong (sky blue, if you're familiar with CharOp ratings) theme for melee characters simply for its level 1 power; anything more than that is just icing on the cake.

Next, consider the statement

you’re supposed to protect people who don’t fight as well as you do.

If the warlock can beat the guardian in a 1-on-1 fight, then this probably does not apply to the warlock. Based on that part of it, I personally would probably rule the warlock to not be a valid bonded charge.

On the other hand, it's not much fun to get a new ability that's entirely useless. Are there any other more reasonable choices available? An NPC that travels with the party? A wizard, invoker, seeker, or psion? Maybe even a bard. If yes, then you're probably on safe ground ruling that the warlock is not a valid target, but the other option is.

If there's nobody else who's even remotely valid as a bonded charge, then consider allowing the player to select the warlock as his bonded charge. You may want to warn him that if the bonded charge ability seems too powerful, or the warlock saves him even half as often as he saves the warlock, then you'll break the bond.

If the warlock has to keep his distance from an attacker, I would be happy to say that a Guardian could bond him.

The seeming intent of the theme is to improve the capabilities of defenders to protect one other party member. Since this is 4E, every PC is supposed to be good at combat. There's just some that fight up close and some that fight at range. Clearly it would be silly if two Guardians could bond each other as their charge, so that would suggest the second quote.

Note that the text says "Generally speaking,". This means that if it is sensible in your game for a particular bodyguard/protectee relationship to exist, you can allow it. Make sure the players understand that it is the existence of the relationship that allows them to use the rule and that it can be dissolved if you think it's necessary. That's a last resort for them acting counter to the relationship and not listening to suggestions they get back to it.

The rules seem pretty clear: the first says you cannot bond someone with greater melee skill, but the latter says you should not bond someone who fights better than you. In any event, certainly seems sensible for a defensive character to protect a squishy ranged character. In general, every player character should be reasonably good at fighting, since that’s most of what they do. Unless Guardian expects that its user will bond an NPC (which may be what is going on, I don’t have the full text in front of me), those rules strike me as kind of dumb.

Again, I don’t have the text in front of me and am not familiar with the Theme, but I suspect I’d allow it.